RFR: Layout updates [v2]

[Per Minborg]

> This PR updates jextract to work with the recent changes in Panama.

Per Minborg has updated the pull request incrementally with two additional commits since the last revision:

 - Fix javadoc
 - Update after comments

-------------

Changes:
  - all: https://git.openjdk.org/jextract/pull/62/files
  - new: https://git.openjdk.org/jextract/pull/62/files/1d57d212..56682b5b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=62&range=01
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=62&range=00-01

  Stats: 16 lines in 3 files changed: 10 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jextract/pull/62.diff
  Fetch: git fetch https://git.openjdk.org/jextract pull/62/head:pull/62

PR: https://git.openjdk.org/jextract/pull/62